Stigmatic imaging of secondary ions in MeV-SIMS spectrometry by linear Time-of-Flight mass spectrometer and the TimePix detector

Abstract : Secondary ion mass spectrometry (SIMS), based on primary ions within the MeV energy domain, also known as MeV-SIMS, is a subject of increasing scientific interest. The main drive for the interest in the development of MeV-SIMS is the ability to desorb high yields of large non-fragmented organic molecular ions from the sample surface. This makes MeV-SIMS particulary useful in imaging of biological tissues. Imaging methods based on scanning a focused primary ion beam are associated with demanding focusing of the heavy energetic ions. As an alternative, stigmatic imaging mode has been studied here, applying point-to-point imaging characteristics of secondary ions in the linear Time-Of-Flight mass spectrometer. In stigmatic imaging approaches, spatial resolution is independent of the focussed spot size of the ionising primary ion beam, but instead dependant on the ability of the ion optics to project an image of the ion distributions removed from the surface onto a position sensitive ion detector.